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Vitamin Tolerance of Animals (1987) / Chapter Skim
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2 Vitamin D
Pages 11-22

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From page 11...
... This information has been fostered by the development of high specific activity, radiolabeled vitamin D, and more precise isolation and identification methods to study vitamin D metabolism in greater detail. NUTRITIONAL ROLE Vitamin D can be considered a vitamin only in the sense that, under modern farming conditions, many animals are raised in total confinement with little or no exposure to natural sunlight.
From page 12...
... 2-D binds to a specific receptor in the enterocyte nucleus and initiates events leading to a stimulation in calcium and phosphorus absorption (Norman et al., 1982~.
From page 13...
... Although its toxicity in humans has been known for more than 40 years, the vitamin's significance in veterinary medicine has drawn greater attention in connection with massive administration to prevent milk fever in ~ airy cows. Clinical signs Many investigators have described the clinical signs of hypervitaminosis D in mammals.
From page 14...
... Therefore, the difference in toxicity between these vitamins is probably attributable to the less efficient metabolism of vitamin D2 to its more active metabolites, particularly 25-OH-D2. In most species, plasma concentrations of 1,25-tOH)
From page 15...
... The route of administration also influences toxicity. Parenteral administration of 15 million IU of vitamin D3 in a single dose caused toxicity and death in many pregnant dairy cows (Littledike and Horst, 1982~.
From page 16...
... Following withdrawal of the vitamin D, the activity in the liver had decreased to normal levels within 2 to 3 weeks. PRESUMED UPPER SAFE LEVELS Existing data for several of the domestic species do not allow precise estimates to be made for maximum vitamin D tolerance levels.
From page 17...
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From page 18...
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From page 19...
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From page 20...
... reported plasma vitamin D and vitamin D metabolite concentrations in several animal species that consumed experimental diets for several months. A retrospective analysis of dietary ingredients indicated that all of the diets consumed by the different species contained 4- to 10-fold the required level of vitamin D3 (National Research Council, 1975, 1978a, 1979, 1984~.
From page 21...
... National Research Council.1978b. Nutrient Requirements of Horses.
From page 22...
... Washington, D.C.: National Academy Press. National Research Council.


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